Xerostomia (dry mouth from decreased salivary flow) is an important health problem contributing to poor nutrition (inability to eat), significantly increased rates of dental caries and other oral infections, inability to wear dentures due to decreased oral moisture, diminished gustatory sensation, difficulty in speech, and very significantly decreased quality of life. Xerostomia is a nearly universal problem following head and neck irradiation for cancer treatment due to the fibrosis and resultant decreased production of saliva by the salivary glands in the irradiated fields. The effect of xerostomia on health and quality of life has been documented in numerous published studies, and is consistently cited by patients as one of the most important long-term side-effects of head and neck irradiation therapy. Current treatments for xerostomia are either only palliative, or medication-based. Those medications which have been shown to be effective have a high rate of significant side effects, and are frequently contraindicated in patients with xerostomia. Recent preliminary evidence indicates that hyperbaric oxygen therapy (HBO2) therapy may significantly and permanently increase salivary flow in patients who have radiation-induced xerostomia, and who receive HBO2 as treatment or preventatively for osteoradionecrosis, or for head and neck soft tissue radiation injury. In this clinical observational study we propose to prospectively examine patients with radiation-induced xerostomia who are undergoing HBO2 therapy for radiation treatment side effects to evaluate the effect of HBO2 on their salivary production status. To achieve the aims of this study we will enroll two groups of patients who have a history of head/neck irradiation and who have xerostomia as a result. One group will be receiving HBO2 for reasons unrelated to their xerostomia, and the other will not be receiving HBO2. Subjects will be evaluated for both objective (salivary production) and subjective (ease of swallowing, speech, dryness, etc.) measures at baseline, weekly during HBO2 therapy (typically 4-8 weeks), and immediately following treatment. These same measures will be repeated at 3 month intervals through the study period. This straightforward study aims to evaluate the effectiveness of a potentially important treatment for radiation-induced xerostomia. Patients who are receiving HBO2 will be assessed for both objective and subjective change in salivary function/oral moisture. Should this treatment prove effective, the data from this study will provide the basis for an R01-type proposal in which we can more fully evaluate the mechanism and effect of HBO2 on salivary function in radiation-induced xerostomia, including long term follow-up measures. Project Narrative: Xerostomia (severe dry mouth) is an important health and quality of life problem, especially for individuals who have received head/neck radiation therapy. There are currently no universally, or even consistently effective treatments, especially when the etiology is from irradiation treatment involving the major salivary glands. Because hyperbaric oxygen treatment (HBO2) appears to have the potential to significantly and permanently improve salivary flow through an actual change in the composition and function of salivary gland tissue, it may prove to provide an important therapeutic option for patients who exhibit xerostomia which is the result of alterations in major salivary gland function due to radiation treatment.